Field of the Invention
The present invention relates to a doctor-type ink fountain for a printing press including a rear wall having at least one flow profile for fluidically influencing the printing ink.
Doctor-type ink fountains of that kind are used in anilox inking units. They interact with a screen roller. A problem may arise if the screen roller has a helical engraving. An undesired effect of an engraving with that shape is that ink is conveyed towards one of the ink fountain ends since the engraving acts like a worm conveyor. The result is an uneven distribution of ink in the ink fountain, which has a negative effect on the quality of the print.
German Patent Application DE 10 2006 002 170 A1, corresponding to U.S. Patent Application Publication No. 2007/0169651, discloses a doctor-type ink fountain in which a rear wall has a flow profile facing the screen roller. The flow profile forms an outer corner, which in cooperation with the circumferential surface of the screen roller, forms a bottleneck. When the printing ink is conveyed towards the bottleneck due to the rotation of the screen roller, the flow profile causes a dynamic pressure of the printing ink in the region of the bottleneck. Due to that dynamic pressure, the engraved depressions or screen depressions (cells or grooves) of the screen roller are filled largely without air inclusion and very evenly. However, the flow profile does not solve the problem explained above. If the screen depressions of the prior art screen roller were of helical shape and if they thus conveyed the ink in a predominant direction, the flow profile in the form of the outer corner would not have any influence thereon at all.
U.S. Pat. No. 4,158,333 describes a doctor-type ink fountain in which a row of vertical plates is provided to improve the flow of ink onto the circumferential surface of the screen roller. The plates are also intended to improve the circulation of ink and to avoid turbulences.
European Patent EP 0 683 730 B1, corresponding to U.S. Pat. No. 5,255,603, describes an ink container including a deflection device. The deflection device includes throttling bodies disposed in a matrix. The document points out that the ink flow caused by the screen roller is directed in a direction corresponding to the direction of rotation of the screen roller. The ink flow may be deflected by the walls of the ink container so that the ink flow is parallel to the axis of rotation of the screen roller.
U.S. Pat. No. 7,607,390 B2 describes a doctor-type ink fountain in which a stirrer moves back and forth in the ink supply to remove air bubbles.
The prior art does not address the problem explained in the introduction to any satisfactory extent.